diff --git a/cluster/defaults.go b/cluster/defaults.go
index ed0b4def..debc4ecb 100644
--- a/cluster/defaults.go
+++ b/cluster/defaults.go
@@ -3,6 +3,7 @@ package cluster
 import (
 	"context"
 	"fmt"
+	"strings"
 
 	"github.com/rancher/rke/cloudprovider"
 	"github.com/rancher/rke/docker"
@@ -100,6 +101,7 @@ func (c *Cluster) setClusterDefaults(ctx context.Context) {
 			c.Nodes[i].Port = DefaultSSHPort
 		}
 
+		c.Nodes[i].HostnameOverride = strings.ToLower(c.Nodes[i].HostnameOverride)
 		// For now, you can set at the global level only.
 		c.Nodes[i].SSHAgentAuth = c.SSHAgentAuth
 	}